Great port. I recognized two issues more in V3.1, which are not in the issue-list above.
First one is, that the game correctly saved my highscore, when i scored more than 30.000 points, but after a restart of the game, my higher score was not correctly displayed at the top of the screen, where the highscore can be seen. There still is the 30.000 score listed as the highscore, although the highscore-list shows my much larger score correctly at the top. So it works in the list, but not in the highscore-display on the screen.
Second thing i recognized is, that sometimes the game has it's little problems with sprite-collisions. I noticed a few times, that i actually hit an enemy with a shot, but maybe because i didn't hit the opponent exactly in the middle, he just kept on flying and ddidn't die. That cost me a few lives and that's not the case in the Arcade original or in the NES and Atari-7800 ports. The shot hit-query sometimes is not precise enough so far and this should be improved.
Then i also noticed some of the other issues mentioned in the list above. So there is still work to do, but from a gameplay point of view, it already looks and plays good. Looking forward to the finalised game.